The invention relates to a fire extinguishing installation comprising a liquid container connected to a gas container by means of a first line for discharging liquid from the liquid container via an outlet of the liquid container and a feed line to at least one spray head, the gas container being connected at a connection point via a second line to the feed line, and a valve one opening of which is connected to the outlet of the liquid container and another opening of which is connected to the feed line. The gas container and the liquid container form a hydraulic accumulator. The fire extinguishing installation of the invention is intended for local or xe2x80x98targetxe2x80x99 extinguishing and it is very well suited to extinguish liquid fires.
JP 11192320 discloses a fire extinguishing installation of the above type. The installation mixes gas and water at a predetermined ratio into a supply pipe. WO 95/28204 discloses a fire fighting installation enabling the mixture of gas with liquid so as to achieve an extinguishing medium, which is a mixture of very small mist-like droplets and gas.
When burning liquids are extinguished at close range and water is used in the local extinguishing as the extinguishing medium, a problem easily arises of the burning liquid being splashed around causing high flames. This problem arises when the burning liquid does not appear as a thin layer but is present in large amounts, typically in an open basin or vessel. The splashing is caused by the extinguishing medium (water) vaporizing and expanding at a high temperature producing a kind of a pressure shock or pressure wave at the surface of the burning liquid. The extinguishing medium can also produce a mechanical xe2x80x98impactxe2x80x99 at the surface of the liquid, causing splashing of the liquid. Even if such a fire, which sometimes resembles an ocean of flame, were extinguished, it causes danger to people nearby and may cause severe burns. Material losses may also be considerable. For example, unsuccessful extinguishing of oil burning in deep-frying pans in restaurants can lead to an ocean of flame with very unfortunate results.
Known fire extinguishing installations are efficient in extinguishing certain types of liquid fires, but their suitability to extinguishing the aforementioned liquid fires susceptible to splashing when extinguishing is not particularly good, although the installation of, for example WO 95/28204 is able to mix gas with liquid immediately at the start when the extinguishing medium starts to flow out of a spray head. This is because the extinguishing medium produced by the installations subjects the surface of the burning liquid to a considerable pressure wave and pressure.
The object of the invention is to provide a fire extinguishing installation operating in two steps and providing fast extinguishing of liquid fires, and especially those involving liquid in deep basins without risk of splashing thanks to the two-step operation and preferably using an environmentally friendly extinguishing medium. The two-step operation of the extinguishing installation is typically such that the installation first supplies a large amount of very small droplets, the total amount of water being, however, very small, after which the droplet size of the extinguishing medium and the amount of liquid therein increase. The former extinguishing step may be called gentle, since it causes no splashing of the burning liquid. A fire is typically extinguished during this step. The second step provides efficient cooling of the target, thus preventing the fire from re-igniting.
This object is achieved with a fire extinguishing installation comprising a liquid container connected to a gas container by means of a first line for discharging liquid from the liquid container via an outlet of the liquid container and a feed line to at least one spray head, the gas container being connected at a connection point via a second line to the feed line, and a valve one opening of which is connected to the outlet of the liquid container and another opening of which is connected to the feed line, wherein the valve is coupled in parallel with the feed line and comprises
a liquid space, connected via a line to the feed line;
an inlet for liquid, connected to the outlet of the liquid container;
a gas space, connected to the second line; and
a spindle arranged between the liquid space and the gas space and movable from a first position, wherein it closes the inlet such that the outlet is not in communication with the liquid space via the inlet, into a second position, wherein it opens the inlet such that the outlet is in communication with the liquid space via the inlet.
Since the pressure in a gas container is preferably high from the point of view of the operation of the extinguishing installation, and the extinguishing medium is not to be supplied to the spray head at too high a pressure, it is recommendable to provide the second line with a first throttle, and arrange a second throttle, coupled in parallel with the valve, between the outlet of the liquid container and the connection point, to connect the liquid space to the feed line at a point located after the second throttle seen in the flow direction of the liquid, and to connect the gas space to the second line between the first throttle and the gas container. Two throttles provide a good operation, but one of said throttles may be omitted from the installation even in high-pressure applications.
The spindle preferably comprises an action surface, on which the liquid pressure acts when the spindle is in the first position, a shoulder surface, on which the liquid pressure acts only when the spindle is in the second position, and a gas space surface, which points at the gas space and is larger than the action surface. Such a spindle acts automatically, i.e. moves, controlled by the pressures acting at any given time in the gas and liquid containers; thus, external energy, e.g. electric energy, is not needed for controlling the valve. The spindle moves from the first position to the second position only when a liquid pressure acts on the action surface, the liquid pressure being significantly higher than the gas pressure acting on the gas space surface. The pressure acting on the gas space surface decreases as the gas container empties; and initially, as the liquid container empties, the liquid pressure acting on the action surface decreases relatively slowly compared with the decrease in the pressure acting on the gas space of the valve. This means that the gas container first supplies gas to the feed line, and the liquid container supplies liquid via the throttle to the feed line until the pressure in the gas container is decreased sufficiently low. When the pressure acting on the gas space surface decreases significantly below the liquid pressure acting on the action surface, the spindle moves from the first position to the second position. The shoulder surface allows the spindle, once it has moved from the first position to the second position, to remain for a while in a position that enables the flow of a large amount of liquid via the liquid space in the valve to the feed line and from there further to the spray head. The valve preferably comprises a spring arranged to load the spindle. The choice of spring affects the operation of the valve, and therefore a spring that has a spring constant suited to the application in question and that loads the spindle in the desired direction is selected.
Preferred embodiments of the invention are disclosed in the attached claims.
The most important advantage of the fire extinguishing installation of the invention is that it is able to first supply extinguishing medium that has a low kinetic energy and very little liquid, which, when expanding in a hot environment, is unable to cause a harmful pressure impact or pressure wave, after which the installation is able to supply extinguishing medium having relatively large drops and relatively much liquid and kinetic energy, said latter extinguishing medium causing further cooling of the fire site. Due to said two-step operation, the extinguishing medium does not break the surface of the burning liquid, which would cause splashing, but extinguishes the fire efficiently immediately at the start. Once the fire is extinguished, the extinguishing medium having much kinetic energy attends to efficient cooling and makes sure the fire does not re-ignite. An extinguishing medium having little kinetic energy contains much gas and relatively little liquid, which is mist-like. An extinguishing medium having much kinetic energy contains much mist-like liquid, the droplet size being, however, larger than in an extinguishing medium having little kinetic energy.